Method and Apparatus for Detecting a Multitouch Event in an Optical Touch-Sensitive Device

1. A method for determining a touch point on a touch-sensitive optical device comprising a plurality of optical emitters and a plurality of optical detectors, the optical emitters and the optical detectors defining therebetween a plurality of optical beam paths forming an optical beam intersection pattern extending over an area, the method comprising the steps of: detecting a modulation of energy in beams transmitted along each of a pair of optical beam paths; assigning a candidate touch point at the intersection of said pair of modulated beams; accessing stored data from a database defining predetermined other beams or predetermined other beam intersections near to or coincident with said candidate touch point, wherein the stored data includes respective weighting and/or proximity values relating to the predetermined other beams or predetermined other beam intersections; analyzing said predetermined other beams based at least in part on said stored data; and responsive to said analysis, determining whether the candidate touch point is an actual touch point.

2. The method of claim 1 , wherein said step of assigning is based on a function of the degree of modulation of the predetermined other beams.

3. The method of claim 2 , wherein the contributions of the predetermined other beams are weighted in said function dependent on the degree of modulation.

4. The method as claimed in claim 3 , wherein the weighting for each predetermined other beam depends upon one or more of a proximity of the predetermined other beam to the candidate touch point; an angle of the predetermined other beam to an angle of the modulated beam defining the candidate touch point; and a number of predetermined other beams.

5. The method as claimed in claim 1 , wherein the beam intersection pattern is symmetrical about at least one axis of the area of optical beam paths, and wherein accessing further comprises: retrieving from the stored data information regarding symmetric beams on one side of said at least one axis; extrapolating the symmetric beam data for the predetermined other beams on a symmetrically opposite side of said at least one axis based on said stored data.

6. The method as claimed in claim 1 , further comprising: designating said modulation as an interruption of the modulated beam if said modulation exceeds a threshold level, and wherein assigning further comprises assigning said candidate touch point responsive to determining that both modulated beams are interrupted.

7. The method as claimed in claim 6 , wherein said threshold level is an adaptive threshold level.

8. The method as claimed in claim 6 , designating comprises comparing the detected modulation with a predefined modulation level for that touch point region.

9. The method as claimed in claim 8 , further comprising retrieving stored data from the database, the stored data including the typical threshold level indicative of a typical modulation level for an actual touch point for that touch point region.

10. The method as claimed in claim 9 , wherein said data comprises one or more of the following: a number of beams passing through the touch point region; a number of intersections of any beams falling within the touch point region; or a maximum modulation to be expected in the touch point region.

11. The method as claimed in claim 1 , further comprising the step of grouping actual touch points into clusters based on a search radius distance from a cluster member to at least one other member of the same cluster.

12. The method as claimed in claim 11 , wherein said beam intersection pattern is non-uniform and said search radius distance varies according to the position of the cluster member in the beam intersection pattern.

13. The method as claimed in claim 11 , further comprising the step of estimating the centre of a cluster as the average position of all of the cluster members.

14. The method as claimed in claim 11 , further comprising the step of estimating the centre of a cluster as the centre of a bounding rectangle around the cluster.

15. The method as claimed in claim 11 , further comprising the step of estimating the centre of a cluster as the average position of outlying cluster members.

16. The method as claimed in claim 13 , wherein said estimation step is based on a weighted average, the weights depending on the degree of modulation of a plurality of beams at each actual touch point contributing to the average.

17. The method as claimed in claim 1 , further comprising determining an orientation of a non-circular touch contact area by mathematically rotating at least two actual touch points lying on or near the perimeter of the contact area around an estimated centre of the contact area and determining a minimum or maximum average absolute value of a distance between each actual touch point and a fixed axis.

18. The method as claimed in claim 1 , comprising the steps of: initialising a point validity value for said candidate touch point; selecting a predetermined other test beam near to or coincident with said candidate touch point; measuring a strength of said predetermined other test beam; calculating an attenuation margin for said predetermined other test beam based on said measured beam strength; multiplying said attenuation margin by a weighting value; adding the weighted attenuation margin to said point validity value; repeating the selecting, measuring, calculating, multiplying, and adding steps for a plurality of predetermined other beams near to or coincident with said candidate touch point; normalizing said point validity value; and responsive to said point validity value exceeding a threshold value, designating said candidate touch point as an actual touch point.

19. The method as claimed in claim 18 , wherein said point validity value is initialised to 0.

20. The method as claimed in claim 18 , wherein calculating further comprises subtracting a threshold value from said measured beam strength.

21. The method as claimed claim in 18 , wherein normalizing further comprises dividing said point validity value by the number of predetermined other beams.

22. The method as claimed in claim 1 , further comprising storing an indication of said actual touch point in a validated point list.

23. The method as claimed in claim 1 , further comprising: determining whether the candidate touch point is near the boundary of a touch event: and wherein said steps of analyzing and determining whether the candidate touch point is an actual touch point are carried out only in respect of those candidate touch point near the boundary of a touch event.

24. A touch-sensitive optical device comprising a plurality of optical emitters and a plurality of optical detectors, the optical emitters and the optical detectors arranged relative to a touchable surface such that energy transmitted by the emitters is received by the detectors along multiple intersecting beams which pass adjacent the surface, and wherein touching the surface at a beam causes a detectable modulation of the energy transmitted along the beam, the device further comprising a processing means operable to perform the following steps: detect a modulation of energy in beams transmitted along each of a pair of optical beam paths; assign a candidate touch point at the intersection of the pair of modulated beams; access stored data from a database defining predetermined other beams or predetermined other beam intersections near to or coincident with said candidate touch point, wherein the stored data includes respective weighting and/or proximity values relating to the predetermined other beams or predetermined other beam intersections; analyze said predetermined other beams based at least in part on said stored data; and responsive to said analysis, determine whether the candidate touch point is an actual touch point.